The present invention is directed toward an ophthalmic device comprising superposed pairs of light polarizing elements, one of such pairs being fixedly retained in a frame member while the elements of the other such pair are rotatable.
The concept of providing variable light transmission characteristics to an ophthalmic device by employing light polarizing elements which may be rotated with respect to each other is not in and of itself novel. For background information on systems of this type, reference should be had to U.S. Pat. No. 2,005,246 issued to E. H. Land on June 18, 1935; U.S. Pat. No. 2,251,330 issued to M. N. Fairbank on Aug. 5, 1941; and U.S. Pat. No. 2,565,362 issued to V. K. Eloranta on Aug. 21, 1951. Each of the foregoing patented inventions, while generally comprising devices for providing variable light transmission by employing light polarizers, have a common problem in that the mechanisms employed to retain the rotatable light polarizing element in engagement with the frame member comprise bearing surfaces which inhibit free axial movement of the rotatable light polarizing elements and introduce enough friction during rotation that binding may occur. Note, for example, FIG. 3 of forementioned U.S. Pat. No. 2,005,426 where elements 13 engage rotatable light polarizing elements 14 and provide bearing surfaces which cause binding of the rotating element. The same problem is evident in the figure of U.S. Pat. No. 2,251,330. Also, FIG. 1 of U.S. Pat. No. 2,565,362 shows that immediately behind rotatable light polarizing elements 64 and 66 is a fiber spacing member 76 which not only provides constraint against axial movement but, as in the other referred to patents, causes binding which inhibits easy rotation of the rotatable elements.